The present invention relates generally to apparatus used to dispense a plurality of liquids through a single orifice, and more particularly it relates to a static mixer used to enhance the mix quality of polyurethane foam from a foam dispenser utilized without the need for solvent cleaning.
Polyurethane foams are formed by the reaction of an isocyanate component and hydroxyl-bearing compounds. When mixed in the presence of a catalyst, a surfactant, and a blowing agent, these chemicals react to form cellular cross-linked polymer chains, more commonly known as a polyurethane foam. Each of these components of the plural component material, by itself, is generally stable. Thus, each component will not cure or cross-link for extended periods of time, often as long as several months, if they are properly stored. However, when the isocyanate component and the polyol component, a preformulated compound that includes a surfactant, a catalyst and a blowing agent, are mixed together in proper proportions, an exothermic chemical reaction of the isocyanate and polyol occurs. This reaction causes a continued expansion that is evidence of the polymerization and manifests itself as foam which cross-links and cures. The cross-linking and curing usually is substantially completed in a matter of seconds.
Polyurethane foam dispensers are well known and have achieved a high degree of usage in insulating or packaging applications. Their use is particularly widespread in the boat manufacturing industry where foam is used to enhance the buoyancy of the watercraft. This type of a manufacturing application requires a low density foam that can be dispensed by apparatus in a potentially combustible or explosive environment. One of the problems with foam dispensing equipment used in the marine industry involves the need to obtain a fully expanded low density foam that has not lost some of its fluorocarbons.
Prior foam dispensing apparatus has employed static mixer attachments made from either metal or plastic, such as by injection molding, that use alternating left and right handed helically-curved baffles to intermix a plurality of fluids. Representative apparatus of this type utilized to mix and blend polymeric fluids include those shown in U.S. Pat. Nos. 3,953,002; 4,408,493; 4,840,493; and 4,850,750. Two banks of stationary non-helical baffle plates arranged around an axis parallel to the overall direction of fluid flow have been used to accomplish the desired mixing and blending, as shown in U.S. Pat. No. 4,093,188. However, these devices do not always yield the desired low density foam needed for marine applications.
These problems are solved in the design of the present invention by providing an improved static mixer design in a plural component dispensing apparatus having a plurality of serially arranged oppositely handed baffle members within a tubular housing with an intermediate spacer portion where the baffle members are interrupted to form a substantially planar connecting portion. The intermediate spacer portion separates the baffle members into two separate mixer sections.